Objects such as wafers may be manufactured by highly complicated manufacturing processes. These manufacturing processes should be monitored in order to ensure the quality of the wafers.
The monitoring process may include a first phase of an optical, ultraviolet, deep ultraviolet, extreme ultraviolet of electron beam inspection to detect potential defects and a second phase of defect review.
Defect review may be usually executed by a scanning electron microscope (SEM) that exhibits a very high resolution (nanometric order). A SEM usually acquires multiple images of the same area (multiple consecutive scans of the area) and then averages these multiple images to provide an output image of the area. The output image can be displayed to an operator. The operator may be expected to evaluate the area in view of the output image.
A high aspect ratio hole such as a deep trench or a deep void, may have an aspect ratio that exceeds 20. The high aspect ratio and the small width of the high aspect ratio hole cause the bottom of the high aspect ratio hole to exhibit a very low electron yield.
The electron yield of the bottom of the high aspect ratio hole may be the ratio between (a) a number of electrons that originate from the bottom of the high aspect ratio hole and may be detected by the SEM as a result of an irradiation of the high aspect ratio hole and (b) the number of electrons that irradiate the high aspect ratio hole.
Other non-limiting examples of low electron yield structures include vertical NAND memory structures and trenches.
Obtaining image of a desired quality may require the SEM to scan an entire area (that includes both high and low electron yield regions) at a very low scan rate.
There may be a growing need to improve the review of areas that include high and low electron yield regions.